Action control is a key brain function determining the survival of animals in their environment. In mammals, neurons expressing dopamine D2 receptors (D2R) in the dorsal striatum (DS) and the nucleus accumbens (Acb) jointly but differentially contribute to the fine regulation of movement. However, their region-specific molecular features are presently unknown. By combining RNAseq of striatal D2R neurons and histological analyses, we identified hundreds of novel region-specific molecular markers, which may serve as tools to target selective subpopulations. As a proof of concept, we characterized the molecular identity of a subcircuit defined by WFS1 neurons and evaluated multiple behavioral tasks after its temporally-controlled deletion of D2R. Consequently, conditional D2R knockout mice displayed a significant reduction in digging behavior and an exacerbated hyperlocomotor response to amphetamine. Thus, targeted molecular analyses reveal an unforeseen heterogeneity in D2R-expressing striatal neuronal populations, underlying specific D2R's functional features in the control of specific motor behaviors.

In the hippocampus, a functional role of dopamine D1 receptors (D1R) in synaptic plasticity and memory processes has been suggested by electrophysiological and pharmacological studies. However, comprehension of their function remains elusive due to the lack of knowledge on the precise localization of D1R expression among the diversity of interneuron populations. Using BAC transgenic mice expressing enhanced green fluorescent protein under the control of D1R promoter, we examined the molecular identity of D1R-containing neurons within the CA1 subfield of the dorsal hippocampus. In agreement with previous findings, our analysis revealed that these neurons are essentially GABAergic interneurons, which express several neurochemical markers, including calcium-binding proteins, neuropeptides, and receptors among others. Finally, by using different tools comprising cell type-specific isolation of mRNAs bound to tagged-ribosomes, we provide solid data indicating that D1R is present in a large proportion of interneurons expressing dopamine D2 receptors. Altogether, our study indicates that D1Rs are expressed by different classes of interneurons in all layers examined and not by pyramidal cells, suggesting that CA1 D1R mostly acts via modulation of GABAergic interneurons.Electronic supplementary materialThe online version of this article (doi:10.1007/s00429-016-1314-x) contains supplementary material, which is available to authorized users.

The phosphorylation of the ribosomal protein S6 (rpS6) is widely used to track neuronal activity. Although it is generally assumed that rpS6 phosphorylation has a stimulatory effect on global protein synthesis in neurons, its exact biological function remains unknown. By using a phospho-deficient rpS6 knockin mouse model, we directly tested the role of phospho-rpS6 in mRNA translation, plasticity and behavior. The analysis of multiple brain areas shows for the first time that, in neurons, phospho-rpS6 is dispensable for overall protein synthesis. Instead, we found that phospho-rpS6 controls the translation of a subset of mRNAs in a specific brain region, the nucleus accumbens (Acb), but not in the dorsal striatum. We further show that rpS6 phospho-mutant mice display altered long-term potentiation (LTP) in the Acb and enhanced novelty-induced locomotion. Collectively, our findings suggest a previously unappreciated role of phospho-rpS6 in the physiology of the Acb, through the translation of a selective subclass of mRNAs, rather than the regulation of general protein synthesis.

Mechanisms of drug-tolerance remain poorly understood and have been linked to genomic but also to non-genomic processes. 5-fluorouracil (5-FU), the most widely used chemotherapy in oncology is associated with resistance. While prescribed as an inhibitor of DNA replication, 5-FU alters all RNA pathways. Here, we show that 5-FU treatment leads to the production of fluorinated ribosomes exhibiting altered translational activities. 5-FU is incorporated into ribosomal RNAs of mature ribosomes in cancer cell lines, colorectal xenografts, and human tumors. Fluorinated ribosomes appear to be functional, yet, they display a selective translational activity towards mRNAs depending on the nature of their 5′-untranslated region. As a result, we find that sustained translation of IGF-1R mRNA, which encodes one of the most potent cell survival effectors, promotes the survival of 5-FU-treated colorectal cancer cells. Altogether, our results demonstrate that “man-made” fluorinated ribosomes favor the drug-tolerant cellular phenotype by promoting translation of survival genes.

Repeated psychostimulant exposure induces persistent gene expression modifications that contribute to enduring changes in striatal GABAergic spiny projecting neurons (SPNs). However, it remains unclear whether changes in the control of mRNA translation are required for the establishment of these durable modifications. Here we report that repeated exposure to D-amphetamine decreases global striatal mRNA translation. This effect is paralleled by an enhanced phosphorylation of the translation factors, eIF2α and eEF2, and by the concomitant increased translation of a subset of mRNAs, among which the mRNA encoding for the activity regulated cytoskeleton-associated protein, also known as activity regulated gene 3.1 (Arc/Arg3.1). The enrichment of Arc/Arg3.1 mRNA in the polysomal fraction is accompanied by a robust increase of Arc/Arg3.1 protein levels within the striatum. Immunofluorescence analysis revealed that this increase occurred preferentially in D1R-expressing SPNs localized in striosome compartments. Our results suggest that the decreased global protein synthesis following repeated exposure to D-amphetamine favors the translation of a specific subset of mRNAs in the striatum.

1 Partial response to chemotherapy leads to disease resurgence. Upon treatment, a subpopulation of 2 cancer cells, called drug-tolerant persistent cells, display a transitory drug tolerance that lead to 3 treatment resistance 1,2 . Though drug-tolerance mechanisms remain poorly known, they have been 4 linked to non-genomic processes, including epigenetics, stemness and dormancy 2-4 . 5-fluorouracil 5 (5-FU), the most widely used chemotherapy in cancer treatment, is associated with resistance. While 6 prescribed as an inhibitor of DNA replication, 5-FU alters all RNA pathways [5][6][7][8][9] . Here, we show that 5-7 FU treatment leads to the unexpected production of fluorinated ribosomes, exhibiting altered mRNA 8 translation. 5-FU is incorporated into ribosomal RNAs of mature ribosomes in cancer cell lines, 9 colorectal xenografts and human tumours. Fluorinated ribosomes appear to be functional, yet, they 10 display a selective translational activity towards mRNAs according to the nature of their 5'-11 untranslated region. As a result, we found that sustained translation of IGF-1R mRNA, which codes 12 for one of the most potent cell survival effectors, promoted the survival of 5-FU-treated colorectal 13 cancer cells. Altogether, our results demonstrate that "man-made" fluorinated ribosomes favour the 14 drug-tolerant cellular phenotype by promoting translation of survival genes. This could be exploited 15 for developing novel combined therapies. By unraveling translation regulation as a novel gene 16 expression mechanism helping cells to survive a drug-challenge, our study extends the spectrum of 17 molecular mechanisms driving drug-tolerance. 18Main text 19Translation regulation plays a major role in controlling gene expression and contributes to diseases 20 emergence including cancer 10,11 . Within ribosomes, ribosomal RNAs (rRNAs) play a central role in the 21 translation process, by monitoring codon:anti-codon recognition, coordinating ribosomal subunit 22 activity and catalysing peptide-bond formation through its ribozyme activity. rRNAs contain over 200 23 naturally occurring chemical modifications which stabilise rRNA structure and create additional 24 molecular interactions not provided by non-modified nucleotides 12-14 . Chemical modifications of 25 rRNAs were shown to directly contribute to translational regulation 11,15,16 . We, and others, showed 26 3 that rRNA chemical modifications contribute to the fine-tuning of ribosome functions and to 1 modulating translational activity of ribosomes in cancer cells [17][18][19][20] . 5-FU treatment results in 5-2 fluorouridine (5-Urd) incorporation into various types of cellular RNA including the precursor of rRNA 3 9 . However, the consequences of 5-FUrd incorporation into ribosomal RNA precursor on ribosome 4 production and functioning have so far not been analysed, neither is its impact on cellular 5 phenotype.6 5-FU does not inhibit ribosome production 7 Previous work indicated that at a high concentration, 5-FU alters ribosome biogenesis without 8 inhibit...

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